Most Cited Surface and Coatings Technology Articles
The most cited articles published since 2011, extracted from Scopus.
Hard nanocomposite coatings: Thermal stability, oxidation resistance and toughnessJ. Musil
Volume 207, Issue , August 2012, Pages 50-65
The article reports on the enhanced hardness of nanocomposite coatings, their thermal stability, protection of the substrate against oxidation at temperatures above 1000°C, X-ray amorphous coatings thermally stable above 1000°C and new advanced hard nanocomposite coatings with enhanced toughness which exhibit (i) low values of the effective Young's modulus E satisfying the condition H/E >0.1, (ii) high elastic recovery W e≥60%, (iii) strongly improved tribological properties, and (iv) enhanced resistance to cracking; here E =E(1-ν 2), E is the Young's modulus and ν is the Poison's ratio. At the end trends of next development of hard nanocomposite coatings are briefly outlined. © 2012 Elsevier B.V.
A review of plasma-assisted methods for calcium phosphate-based coatings fabricationRoman A. Surmenev
Volume 206, Issues 8-9, January 2012, Pages 2035-2056
The review is focused on the latest achievements in the field of plasma-assisted fabrication of biocompatible CaP-based coatings for medical implants with the emphasis on the coatings composition, structure, mechanical and biological performance. The discussed properties of biocompatible CaP coatings have been recently prepared using the most frequently applied plasma-assisted techniques such as plasma spraying (PS), radio-frequency (RF) magnetron sputtering, pulsed laser deposition (PLD), and ion beam-assisted deposition (IBAD). The review shows that plasma-assisted fabrication allows us to prepare dense, homogeneous, pore-free and high adherent biocompatible coatings able to prevent the leaching of toxic ions from metal to the surrounding tissues or rough and porous coatings capable of stimulating osteogenesis of a new bone. The main advantages and limitations of the described techniques of CaP-based coatings fabrication are presented as well as the most important challenges and critical issues are highlighted. © 2011 Elsevier B.V.
The effect of current mode and discharge type on the corrosion resistance of plasma electrolytic oxidation (PEO) coated magnesium alloy AJ62R. O. Hussein | P. Zhang | X. Nie | Y. Xia | D. O. Northwood
Volume 206, Issue 7, December 2011, Pages 1990-1997
Magnesium alloys are increasingly being used as lightweight materials in the automotive, defense, electronics, biomaterial and aerospace industries. However, their inherently poor corrosion and wear resistance have, so far, limited their application. Plasma electrolytic oxidation (PEO) in an environmentally friendly aluminates electrolyte has been used to produce oxide coatings with thicknesses of ~. 80 μm on an AJ62 magnesium alloy. Optical emission spectroscopy (OES) in the visible and near ultraviolet (NUV) band (285. nm-800. nm) was employed to characterize the PEO plasma. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the coated materials, and potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a 3.5% NaCl solution were used to determine the corrosion behavior. It was found that the plasma discharge behavior significantly influenced the microstructure and the morphology of the oxide coatings and, hence the corrosion resistance. The corrosion resistance of the coated alloy was increased by changing the current mode from unipolar to bipolar, where the strong plasma discharges had been reduced or eliminated. © 2011 Elsevier B.V.
Discharge physics of high power impulse magnetron sputteringAndré Anders
Volume 205, Issue SUPPL. 2, July 2011, Pages S1-S9
High power impulse magnetron sputtering (HIPIMS) is pulsed sputtering where the peak power exceeds the time-averaged power by typically two orders of magnitude. The peak power density, averaged over the target area, can reach or exceed 107W/m2, leading to plasma conditions that make ionization of the sputtered atoms very likely. A brief review of HIPIMS operation is given in a tutorial manner, illustrated by some original data related to the self-sputtering of niobium in argon and krypton. Emphasis is put on the current-voltage-time relationships near the threshold of self-sputtering runaway. The great variety of current pulse shapes delivers clues on the very strong gas rarefaction, self-sputtering runaway conditions, and the stopping of runaway due to the evolution of atom ionization and ion return probabilities as the gas plasma is replaced by metal plasma. The discussions are completed by considering instabilities and the special case of "gasless" self-sputtering. © 2011 Elsevier B.V.
Induction plasma sprayed nano hydroxyapatite coatings on titanium for orthopaedic and dental implantsMangal Roy | Amit Bandyopadhyay | Susmita Bose
Volume 205, Issues 8-9, January 2011, Pages 2785-2792
This paper reports preparation of a highly crystalline nano hydroxyapatite (HA) coating on commercially pure titanium (Cp-Ti) using inductively coupled radio frequency (RF) plasma spray and their in vitro and in vivo biological response. HA coatings were prepared on Ti using normal and supersonic plasma nozzles at different plate powers and working distances. X-ray diffraction (XRD) and Fourier transformed infrared spectroscopic (FTIR) analysis show that the normal plasma nozzle lead to increased phase decomposition, high amorphous calcium phosphate (ACP) phase formation, and severe dehydroxylation of HA. In contrast, coatings prepared using supersonic nozzle retained the crystallinity and phase purity of HA due to relatively short exposure time of HA particles in the plasma. In addition, these coatings exhibited a microstructure that varied from porous and glassy structure at the coating-substrate interface to dense HA at the top surface. The microstructural analysis showed that the coating was made of multigrain HA particles of ~. 200. nm in size, which consisted of recrystallized HA grains in the size range of 15-20. nm. Apart from the type of nozzle, working distance was also found to have a strong influence on the HA phase decomposition, while plate power had little influence. Depending on the plasma processing conditions, a coating thickness between 300 and 400 μm was achieved where the adhesive bond strengths were found to be between 4.8 and 24. MPa. The cytotoxicity of HA coatings was examined by culturing human fetal osteoblast cells (hFOB) on coated surfaces. In vivo studies, using the cortical defect model in rat femur, evaluated the histological response of the HA coatings prepared with supersonic nozzle. After 2. weeks of implantation, osteoid formation was evident on the HA coated implant surface, which could indicate early implant-tissue integration in vivo. © 2010.
Surface design of biodegradable magnesium alloys - A reviewGuosong Wu | Jamesh Mohammed Ibrahim | Paul K. Chu
Volume 233, Issue , October 2013, Pages 2-12
Biodegradability is a big advantage of magnesium-based materials in biomedical applications such as bone fixation, cardiovascular stents, and even stomach trauma repair. Different from other metals such as stainless steels and Ti alloys, the interface between the Mg-based implants and biological environment is dynamic. In order to improve the surface properties to allow better and more expeditious adaptation to the physiological surroundings, it is imperative to design and construct a surface to satisfy multiple clinical requirements such as mechanical strength, biocompatibility, and degradation rate. This paper reviews recent work pertaining to surface modification of Mg-based biomaterials with emphasis on surface coatings and ion implantation. The biodegradation behavior and related mechanism in the physiological environment after surface modification are also described. Surface modification is a promising means to elevate the performance of Mg-based biomaterials and expected to be extensively applied to surface design of biomaterials. © 2012 Elsevier B.V.
Friction and wear characteristics of multi-layer graphene films investigated by atomic force microscopyLi Yu Lin | Dae Eun Kim | Whan Kyun Kim | Seong Chan Jun
Volume 205, Issue 20, July 2011, Pages 4864-4869
Friction and wear characteristics of multi-layer graphene films deposited on a Si substrate by mechanical exfoliation were investigated by atomic force microscopy (AFM). The graphene films consisted of a few layers of carbon basal plane. The number of graphene layers was determined by AFM and Raman spectroscopy. For the AFM friction measurement, loads in the range of -5 to 30. nN were applied on the Si tip that slid against the graphene specimen. It was found that graphene films exhibited much lower friction (from 0.36 to 0.62. nN) than bare Si surface (from 1.1 to 4.3. nN) when the applied loads ranged from 3 to 30. nN. The wear characteristics were also assessed using the AFM. Detectable wear of graphene was generated when sliding was performed for 100. cycles under 5 μN applied load. The wear mechanism of graphene was proposed to be due to breakage of in-plane bonds between carbon atoms and shearing at the interface of graphene layers. © 2011 Elsevier B.V.
A comparative study of titanium nitride (TiN), titanium oxy nitride (TiON) and titanium aluminum nitride (TiAlN), as surface coatings for bio implantsB. Subramanian | C. V. Muraleedharan | R. Ananthakumar | M. Jayachandran
Volume 205, Issues 21-22, August 2011, Pages 5014-5020
In the present study, the performance of three titanium nitride coatings: TiN, TiON, and TiAlN for biomedical applications were assessed in terms of their surface properties electrochemical corrosion in simulated body fluid and cytotoxicity. Layers of TiN, TiON and TiAlN were deposited onto CP-Ti substrates by DC reactive magnetron sputtering method using a combination of a Ti, Ti-Al targets and an Ar-N2 mixture discharge gas. The presence of different phases was identified by XRD analysis. The morphology was determined through atomic force microscopy (AFM) imaging. The XPS survey spectra on the etched surfaces of TiN film exhibited the characteristic Ti2p, N1s, O1s peaks at the corresponding binding energies 454.5, 397.0, and 530.6eV respectively. The characteristic Raman peaks were observed from the Laser Raman spectrometer. Platelet adhesion experiments were done to examine the interaction between blood and the materials in vitro. On Control samples (CP Ti), platelets were seen as aggregates, whereas on coated samples, platelets were seen as singles, without any significant spreading. Cytocompatibility studies of coated samples were carried out with bare titanium (CP Ti - ASTM B 348) as controls. L-929 mouse fibroblast cells were used for samples. All materials showed good cytocompatbility with cell lines used. © 2011 Elsevier B.V.
Effect of electrodeposition conditions and reinforcement content on microstructure and tribological properties of nickel composite coatingsTushar Borkar | Sandip P. Harimkar
Volume 205, Issues 17-18, May 2011, Pages 4124-4134
In this work, pure nickel and nickel composite coatings (Ni-Al2O3, Ni-SiC, and Ni-ZrO2) were deposited from Watts bath using direct current (DC), pulsed current (PC), and pulsed reverse current (PRC) electrodeposition conditions. Detailed investigations on the effect of deposition conditions on the evolution of surface microstructure, crystallographic micro-texture, microhardness, and sliding wear behavior of pure nickel and nickel composite coatings are presented. For all the coatings, the PC and PRC deposition conditions resulted in more random/weak crystallographic texture compared to DC deposition. The composite coatings deposited using PC and PRC deposition also exhibited significant improvement in microhardness and wear resistance due to enhanced reinforcement of nanoparticles in the coatings. Also, the effect of nanoparticle content of the electrolyte bath on the surface microstructure, tribological properties, and level of reinforcement in the Ni-Al2O3 composite coating is investigated. The reinforcement of nanoparticles in the Ni-Al2O3 composite coatings increased linearly with the amount of nanoparticle loading in the electrolyte bath. The microhardness and wear resistance of the Ni-Al2O3 composite coatings also improved with increasing Al2O3 content in the coatings. © 2011 Elsevier B.V.
Numerical modelling of shot peening process and corresponding products: Residual stress, surface roughness and cold work predictionG. I. Mylonas | G. Labeas
Volume 205, Issue 19, June 2011, Pages 4480-4494
An investigation of the effects of controlled shot peening (CSP) process parameters on the treated material is presented. For this purpose, a three dimensional numerical model is developed, comprising the target plate and a number of shot impacts; their number is defined as the minimum required for a realistic simulation and minimum computational cost. The numerical model is verified by comparing the predicted residual stress (RS) fields to experimental. A parametric study of the shot velocity and impinging angle on the CSP products is performed for 4 shot types, i.e. S110, S230, S330 and S550. The main advantages of the present numerical model are: a) the relatively high number of shots introduced in the simulation compared to other publications that use only one shot, b) the number of shots dependency on the desired coverage, c) the thorough selection of numerical parameters, d) the high-strain rate material behaviour used for the target plate, e) the capability to calculate CSP effects on the target plate as function of coverage, f) the computed data which include RS field, surface roughness, cold work and geometrical stress concentration factor (Kt) and finally g) the computed results which are validated by experimental measurements. © 2011 Elsevier B.V.
Electrochemical response of ZrO2-incorporated oxide layer on AZ91 Mg alloy processed by plasma electrolytic oxidationKang Min Lee | Ki Ryong Shin | Seung Namgung | Bongyoung Yoo | Dong Hyuk Shin
Volume 205, Issues 13-14, March 2011, Pages 3779-3784
ZrO2 nanoparticles well dispersed in an electrolyte were effectively incorporated in an oxidized surface passivation layer on AZ91 Mg alloy by a plasma electrolytic oxidation (PEO) process. The electrophoretic reaction and mechanical mixing in molten magnesium oxide were the main factors leading to incorporation of ZrO2 nanoparticles in the magnesium oxide layer. Incorporated ZrO2 nanoparticles were mainly located in pores that were generated during the PEO process. The results of a potentiostatic polarization analysis and a salt spray test clearly indicated that the corrosion resistance of the PEO treated layer was significantly improved by the incorporation of ZrO2 nanoparticles. © 2011 Elsevier B.V.
Synthesis of anodic aluminum oxide (AAO) at relatively high temperatures. Study of the influence of anodization conditions on the alumina structural featuresWojciech J. Stȩpniowski | Zbigniew Bojar
Volume 206, Issues 2-3, October 2011, Pages 265-272
Anodic aluminum oxide (AAO) is a well known template for nanofabrication. Structural features of AAO like pore diameter, interpore distance, porosity, pore density can be fully controlled by operating conditions of anodization. Typically, self-organized two-step anodization is carried out at low temperature (below room temperature) and is a time consuming process. There are individual experiments describing anodization at temperatures close to room temperature. In our study, furthermore, a systematic analysis of the anodization condition influence on the nanoporous alumina structural features was done. The anodization temperature was ranging from 35 to 50. °C increasing significantly current density of the processes, which has increased oxide film growth rate. The anodizing potential ranged from 20 to 60 V and time of the anodization steps was 30, 60 or 120 min. The data obtained has shown that the pore diameter increases with potential, temperature and time of anodization, while the interpore distance is influenced solely by the potential. Temperature and time changes do not affect the interpore distance. Porosity is also influenced by potential, temperature and duration of anodization. Pore density is influenced only by the potential. The synthesis of AAO reported here gives possibilities to obtain the AAO templates in a faster and cheaper way, essential for researchers applying anodic alumina as a template. © 2011 Elsevier B.V.
Oxidation failure of TBC systems: An assessment of mechanismsH. E. Evans
Volume 206, Issue 7, December 2011, Pages 1512-1521
The spallation of thermal barrier coatings can be life-limiting but its prediction has proven to be a difficult problem. The final spallation event can often occur by buckling and is driven by the release of strain energy within the ceramic top coat and within the underlying thermally-grown oxide (TGO) layer if the delamination interface is at the TGO/bond-coat interface. Prior to this event, substantial sub-critical damage must develop at one or both of the TGO interfaces. It is argued in this paper that it is only the strain energy within the TGO produced during cooling that contributes significantly to this damage development and not that within the top coat. A critical strain energy within the TGO layer is suggested as a possible pragmatic method of predicting spallation. A critical assessment of proposed mechanisms which implicate bond coat oxidation in the failure process is also undertaken in the paper. Attention is given to: the role of phase changes in the bond coat; the influence of the mechanical constraint imposed by the top coat on the mechanical stability of the bond coat interface; the effect of the growth of the TGO on a non-planar interface on stress development; the importance of localised Al depletion in nucleating a fast-growing non-protective TGO. © 2011 Elsevier B.V.
Characterization of calcium-modified zinc phosphate conversion coatings and their influences on corrosion resistance of AZ31 alloyRongchang Zeng | Zidong Lan | Linghong Kong | Yuanding Huang | Hongzhi Cui
Volume 205, Issue 11, February 2011, Pages 3347-3355
Two kinds of phosphate conversion coatings, including zinc phosphate coating and zinc-calcium phosphate coating, were prepared on the surface of AZ31 alloy in phosphate baths. The morphologies of these coatings were observed using scanning electron microscopy. Their chemical compositions and structures were characterized using energy-dispersive X-ray spectrum, X-ray photoelectron spectroscopy and X-ray diffraction. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization technique. The results show that the flowerlike Zn-Ca phosphate conversion coatings are mainly composed of hopeite (Zn3(PO4)2·4H2O). They have a quite different morphology from the dry-riverbed-like Zn phosphate coatings that consist of MgO, MgF2, Zn or ZnO and hopeite. Both of the zinc and zinc-calcium phosphate coatings can remarkably reduce the corrosion current density of the substrates. The Zn-Ca coating exhibits better corrosion resistance than the Zn coating. Introduction of calcium into the phosphate baths leads to the full crystallinity of the Zn-Ca coating. © 2010 Elsevier B.V.
Phosphate-permanganate conversion coatings on the AZ81 magnesium alloy: SEM, EIS and XPS studiesM. Mosiałek | G. Mordarski | P. Nowak | W. Simka | G. Nawrat | M. Hanke | R. P. Socha | J. Michalska
Volume 206, Issue 1, October 2011, Pages 51-62
Conversion coatings on the magnesium alloy AZ81 were prepared using the phosphate-permanganate baths differing in composition. The corrosion behavior of the coated and uncoated alloys has been investigated by electrochemical impedance spectroscopy (EIS) and linear polarization methods. The choice of proper electric equivalent circuit (EEC) is discussed. The effect of temperature, bath composition and time of conversion as well as etching in acids before application on the corrosion resistance of the coated alloy has been evaluated. The best corrosion resistance was obtained for the samples coated in the bath containing 25g KMnO4, 150g Na2HPO4 and 50ml H3PO4 in 1 dcm3, applied at 80°C. Differences in the morphology and composition of coated surfaces were investigated by the scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques and correlated with the corrosion resistance of the samples. © 2011 Elsevier B.V.
Review on self-lubricant transition metal dichalcogenide nanocomposite coatings alloyed with carbonT. Polcar | A. Cavaleiro
Volume 206, Issue 4, November 2011, Pages 686-695
In this paper, we review the results on the tribological behavior of nanocomposite coatings composed of nanoplatelets of transition metal dichalcogenides (TMD) immersed in a C-rich amorphous matrix. It is shown that such a microstructure produces low friction coefficients under different operating conditions such as air humidity, contact pressure or temperature. Special attention is paid to the analysis of the worn surfaces after the tests by Raman spectroscopy, Auger electron spectroscopy and transmission electron microscopy. Nanoscale analysis of the wear track has revealed the formation of a thin tribolayer exclusively consisting of TMD platelets oriented to exhibit the lowest friction. In some cases, the depth reorientation of the originally randomly oriented TMD platelets as a reaction to the sliding process has been observed. This self-adaptation explains the low friction coefficient together with a high load-bearing capacity and a limited sensitivity to air humidity. Finally, future perspectives for self-lubricant nanocomposite coatings based on the TMD-C concept are presented. © 2011 Elsevier B.V.
Electrophoretic deposition of chitosan/45S5 Bioglass® composite coatings for orthopaedic applicationsF. Pishbin | A. Simchi | M. P. Ryan | A. R. Boccaccini
Volume 205, Issues 23-24, September 2011, Pages 5260-5268
This article presents experimental results on the electrophoretic deposition (EPD) of bioresorbable chitosan/45S5 Bioglass® composite coatings for orthopaedic implants based on the Taguchi design of experiments (DOE) approach. The influence of EPD parameters including Bioglass® concentration, electric voltage and deposition time on deposition yield was studied by an orthogonal Taguchi array of L18 type. Multivariate analysis of variance (MANOVA) and regression analysis based on the partial least-square method were used to identify the significant factors affecting the deposition yield and its stability during constant-voltage EPD. The coatings were characterised by high resolution scanning electron microscope (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). It is shown that the co-deposition of polymer/Bioglass® system is very sensitive to the concentration of Bioglass® particles. The addition of Bioglass® to the chitosan suspension alters the deposition rate due to variation of pH, suspension conductivity, and zeta potential. For low Bioglass® concentrations, co-deposition of the chitosan and the bioactive glass particles occurs while at the higher concentrations massive deposition of the bioactive glass particles controls the deposition yield. The optimum condition for a high deposition rate with low standard deviation and homogeneous microstructure is achieved when an almost equal concentrations of chitosan and Bioglass® is utilized. The validity of the approach is shown by confirmation experiments at the predicted optimal condition, and the mechanism of electrophoretic co-deposition of the polymer/glass system is discussed. © 2011 Elsevier B.V.
Electrodeposition of Ni-Co alloys from a deep eutectic solventY. H. You | C. D. Gu | X. L. Wang | J. P. Tu
Volume 206, Issue 17, April 2012, Pages 3632-3638
Pure Ni and three Ni-Co alloys films, i.e. Ni-4wt.%Co, Ni-18wt.%Co, and Ni-40wt.%Co, are electrodeposited at room temperature from the choline chloride/ethylene glycol deep eutectic solvent dissolved by nickel or/and cobalt chlorides. Electrodeposition mechanism, microstructure, and corrosion properties of the films are investigated. Surface morphology and chemical composite of the films are significantly dependent on the Ni 2+ and Co 2+ concentrations in the electrolytes. Interestingly, it is found that the amount of cobalt in the Ni-Co alloy films is significantly lower than that present in the electrolytes, which indicates an absence of anomalous codeposition process for the non-aqueous electrolytes. However, anomalous codeposition of Ni-Co deposits is frequently observed for the aqueous electrolytes. The Ni-Co alloy films possess face-centered cubic structures and refined grains revealed by X-ray diffractometer and scanning electron microscope. Potentiodynamic polarization measurements show that the Ni film exhibits the noblest corrosion potential and the lowest corrosion current compared with the Ni-Co alloys films. Moreover, the more Co content the Ni-Co films have, the more negative corrosion potential and the higher corrosion current the films exhibit. © 2012.
Aerosol deposition of hydroxyapatite-chitosan composite coatings on biodegradable magnesium alloyByung Dong Hahn | Dong Soo Park | Jong Jin Choi | Jungho Ryu | Woon Ha Yoon | Joon Hwan Choi | Hyoun Ee Kim | Seong Gon Kim
Volume 205, Issues 8-9, January 2011, Pages 3112-3118
Magnesium (Mg) and its alloys are potential biometallic materials for their good biocompatibility and excellent biological performances. However, Mg alloys corrode too quickly in chloride containing solutions, including the human body fluid and blood plasma, which may result in the abrupt failure of implants made of Mg alloys. Dense and well-adherent HA-chitosan composite coatings were deposited on AZ31 Mg alloy substrate using aerosol deposition (AD) in order to improve both the corrosion resistance and biocompatibility of AZ31 Mg alloy. The HA-chitosan composite powders having chitosan contents of up to 20. wt.% were prepared by a simple dry-powder mixing process and then used for coating by AD. The coatings obtained from the corresponding powders were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and electrochemical measurement. The results revealed that the coating layers had similar compositions to the corresponding powders and exhibited fairly dense microstructures and, hence, AD was found to be a very effective method for the fabrication of dense ceramic-polymer composite coatings with a well-controlled composition. All of the coatings exhibited high adhesion strengths ranging from 24.6 to 27.7. MPa and showed higher corrosion resistances than the bare AZ31 Mg substrate, implying that the corrosion resistance of AZ31 Mg alloy is enhanced by the HA-chitosan composite coating deposited using AD. In addition, the biocompatibility of the alloy was remarkably improved by the HA coating and the incorporation of chitosan into the coating. © 2010 Elsevier B.V.
Hydroxyapatite coating of AZ31 magnesium alloy by a solution treatment and its corrosion behavior in NaCl solutionSachiko Hiromoto | Masanari Tomozawa
Volume 205, Issue 19, June 2011, Pages 4711-4719
Hydroxyapatite (HAp) coatings were formed directly on AZ31 magnesium alloy and pure Mg in a 250mmol/L C10H12N2O8Na2Ca aqueous solution of pH 8.9. Treatment time was varied from 2h to 6h. Crystal phase, morphology and composition of the coatings were investigated. Immersion and polarization tests in a 3.5wt.% NaCl solution were performed to examine the corrosion behavior of the HAp-coated specimens. The HAp coating of AZ31 with short treatment time had defects which decreased with an increase in treatment time. The HAp coatings of AZ31 consisted of an inner dense layer and an outer coarse layer in the similar manner for pure Mg. The inner layer on AZ31 was composed of dome-shape precipitates densely packed. The outer layer was composed of rod-like crystals growing from each dome in the radial direction. The (002) plane of HAp of inner layer and rod-like crystals roughly oriented to the substrate. Magnesium ion-release and corrosion current density were remarkably reduced with HAp coatings. Each of these values was on the same order of magnitude between HAp-coated AZ31 and pure Mg. The ion release from AZ31 slightly decreased with an increase in treatment time. The original inner dense layer of AZ31 remained after the immersion. It is suggested that the protectiveness of HAp coating relays on the inner layer and does not significantly depend on the kind of Mg substrate. © 2011 Elsevier B.V.
High rate deposition of thick CrN and Cr2N coatings using modulated pulse power (MPP) magnetron sputteringJianliang Lin | William D. Sproul | John J. Moore | Sabrina Lee | Sterling Myers
Volume 205, Issue 10, February 2011, Pages 3226-3234
As a variation of high power pulsed magnetron sputtering technique, modulated pulse power (MPP) magnetron sputtering can achieve a high deposition rate while at the same time achieving a high degree of ionization of the sputtered material with low ion energies. These advantages of the MPP technique can be utilized to obtain dense coatings with a small incorporation of the residual stress and defect density for the thick coating growth. In this study, the MPP technique has been utilized to reactively deposit thick Cr2N and CrN coatings (up to 55μm) on AISI 440C steel and cemented carbide substrates in a closed field unbalanced magnetron sputtering system. High deposition rates of 15 and 10 μm per hour have been measured for the Cr2N and CrN coating depositions, respectively, using a 3kW average target power (16.7W/cm2 average target power density), a 50mm substrate to target distance and an Ar/N2 gas flow ratio of 3:1 and 1:1. The CrN coatings showed a denser microstructure than the Cr2N coatings, whereas the Cr2N coatings exhibited a smaller grain size and surface roughness than those of the CrN coatings for the same coating thickness. The compressive residual stresses in the CrN and Cr2N coatings increased as the coating thickness increased to 30μm and 20μm, respectively, but for thicker coatings, the stress gradually decreased as the coating thickness increased. The CrN coatings exhibited an increase in the scratch test critical load as the thickness was increased. Both CrN and Cr2N coatings showed a decrease in the hardness and an increase in the sliding coefficient of friction as the coating thickness increased from 2.5 to 55μm. However, the wear rate of the CrN coatings decreased significantly as the coating thickness was increased to 10μm or higher. The 10-55μm CrN coating exhibited low wear rates in the range of 3.5-5×10-7mm-N-1m-1. To the contrary, the Cr2N coating exhibited relatively low wear resistance in that high wear rates in the range of 3.5 to 7.5×10-6mm3N-1m-1 were observed for different thicknesses. © 2010.
Atmospheric plasma sprayed thermal barrier coatings with high segmentation crack densities: Spraying process, microstructure and thermal cycling behaviorM. Karger | R. Vaßen | D. Stöver
Volume 206, Issue 1, October 2011, Pages 16-23
Thermal barrier coatings (TBCs) with high strain tolerance are favorable for application in hot gas sections of aircraft turbines. To improve the strain tolerance of atmospheric plasma sprayed (APS) TBCs, 400μm-500μm thick coatings with very high segmentation crack densities produced with fused and crushed yttria stabilized zirconia (YSZ) were developed. Using a Triplex II plasma gun and an optimized spraying process, coatings with segmentation crack densities up to 8.9cracksmm-1, and porosity values lower than 6% were obtained. The density of branching cracks was quite low which is inevitable for a good inter-lamellar bonding. Thermal cycling tests yielded promising strain tolerance behavior for the manufactured coatings. Samples with high segmentation crack densities revealed promising lifetime in burner rig tests at rather high surface (1350. °C) and bondcoat temperatures (up to 1085. °C), while coatings with lower crack densities had a reduced performance. Microstructural investigations on cross-sections and fracture surfaces showed that the segmentation crack network was stable during thermal shock testing for different crack densities. The main failure mechanism was delamination and horizontal cracking within the TBC near the thermal grown oxide layer (TGOs) and the TBC. © 2011 Elsevier B.V.
Electromagnetic shielding and corrosion resistance of electroless Ni-P/Cu-Ni multilayer plated polyester fabricS. X. Jiang | R. H. Guo
Volume 205, Issues 17-18, May 2011, Pages 4274-4279
Nickel-phosphorus/copper-nickel (Ni-P/Cu-Ni) multilayers are electroless deposited onto polyester fabric as a function of the deposition time of Ni-P and compared with Ni-P and Cu-Ni deposits. Their surface morphology, microstructure and composition are analyzed by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX). Their electromagnetic interference (EMI) shielding effectiveness (SE) is evaluated and corrosion resistance is characterized by electrochemical polarization measurements. The results show that with the same weight of the deposits, the EMI SE of the Ni-P/Cu-Ni plated fabric is higher than that of the Ni-P plated fabric, while the corrosion resistance of the Ni-P/Cu-Ni plated fabrics is better than the Cu-Ni plated fabrics. Ni-P improves corrosion resistance and greatly enhances the electromagnetic shielding property of Ni-P/Cu-Ni deposits. Furthermore, the EMI SE and corrosion resistance of the Ni-P/Cu-Ni deposits increase with the rise of deposition time of Ni-P. Therefore, electroless Ni-P/Cu-Ni plated fabric is the most appropriate material that will meet the requirements of both corrosion resistance and EMI SE in most textile applications. © 2011 Elsevier B.V.
Improving carbon fiber adhesion to polyimide with atmospheric pressure plasma treatmentJianfei Xie | Danwei Xin | Hongyan Cao | Cuntao Wang | Yi Zhao | Lan Yao | Feng Ji | Yiping Qiu
Volume 206, Issues 2-3, October 2011, Pages 191-201
Plasma treatment is frequently used to modify carbon fiber surfaces to improve adhesion of the fiber to matrices although it may also influence carbon fiber tensile strength. In order to determine the effect of atmospheric pressure plasma treatment on carbon fiber tensile strength and interfacial bonding strength to polyimide, polyacrylonitrile (PAN) based carbon fibers are treated with atmospheric pressure oxygen/helium plasmas for different durations. Tensile strength change of the fiber is studied at different gage lengths before and after the plasma treatment. Interfacial bonding between the carbon fiber and a thermoplastic polyimide matrix is evaluated using a single fiber composite test system. Weibull analysis of the single fiber tensile test data shows no obvious changes in the tensile strength at short gage lengths after plasma treatment while the fiber strength tends to decrease at larger gage lengths. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that the plasma treatments roughen the fiber surfaces. X-ray photoelectron spectroscopy (XPS) analysis of fiber surface shows a significant increase of oxygen concentration after plasma treatment and the oxygen containing functional groups reach their maximum levels after 32 s treatment time and further increasing treatment time does not achieve a higher level of oxidation. Plasma treatments decrease dynamic water contact angles and increase the surface energy of the carbon fibers as measured by the modified Wilhelmy method. The interfacial shear strength is improved 21% after the atmospheric pressure plasma treatment for 32 s. It is concluded that the increase of oxygen containing functional groups and changing of the surface topology may contribute collectively to the improvement of fiber/resin interfacial adhesion. © 2011 Elsevier B.V.
Biomedical investigation of CNT based coatingsXiaoming Li | Xi Liu | Jin Huang | Yubo Fan | Fu zhai Cui
Volume 206, Issue 4, November 2011, Pages 759-766
Owing to their unique properties, carbon nanotubes (CNTs) have emerged as a promising material for biomedical applications. Especially, CNT based coatings have recently made great achievements, which have been mainly stated in this review. They can offer favorable condition to induce the cellular functions. They can possess excellent packing density without any macroscopic porosity within the film on metals. The good bonding strength between them and the metal substrates could be achieved. Addition of CNTs can reinforce the composite coatings and the CNTs-reinforced coatings are expected to be promising for high load-bearing orthopedic implants. Furthermore, based on their unique properties, CNTs can attach to the surfaces of dentin and cementum but not to the surface of enamel, suggesting that the teeth coated with CNTs should be a possible candidate for dental materials. In addition, CNTs can be coated on polymers, bioglasses, collagen, etc. to prepare bioactive, electrically conductive 3D scaffolds for tissue engineering. Besides the current achievements, CNT based coatings possess big space to further develop, such as functionalized CNT based coatings, mineralized CNT coatings, etc., which suggesting that CNTs coatings have emerged as promising methods and potentially reward opportunities to develop the next generation of engineered materials for biomedical applications. © 2011 Elsevier B.V.